Researchers studied 81 people receiving kidney dialysis treatment in Toronto to understand how vitamin D affects muscle strength. They found that people with low vitamin D levels were more than five times likely to have weak grip strength compared to those with normal vitamin D. Interestingly, while almost everyone in the study wasn’t getting enough vitamin D from food alone, taking vitamin D supplements helped raise blood vitamin D levels. The study suggests that maintaining healthy vitamin D levels through supplements may be important for keeping muscles strong in people undergoing dialysis treatment.

The Quick Take

  • What they studied: Whether vitamin D levels in the blood are connected to muscle strength in people receiving kidney dialysis treatment
  • Who participated: 81 adults (average age 58 years, 64% male) from two kidney dialysis centers in Toronto, Canada, representing diverse ethnic backgrounds
  • Key finding: People with low vitamin D had more than 5 times greater chance of having weak hand grip strength compared to those with normal vitamin D levels
  • What it means for you: If you receive kidney dialysis, checking your vitamin D levels and taking supplements if needed may help maintain your muscle strength. However, this study shows a connection, not proof that vitamin D supplements will definitely make you stronger—more research is needed to confirm this.

The Research Details

This was a cross-sectional study, which means researchers looked at a group of people at one point in time rather than following them over months or years. The 81 participants came to two dialysis centers in Toronto and had their muscle strength tested using a hand grip strength test (like squeezing a special device). Researchers also measured vitamin D levels in their blood and asked them to keep food and supplement diaries for three days to track what they were eating and taking.

The researchers used statistical methods to look for connections between vitamin D levels and muscle strength, while accounting for factors like age, sex, and body weight that might also affect results. This approach helps isolate the relationship between vitamin D and muscle strength specifically.

This research approach is important because kidney dialysis patients often have both low vitamin D and weak muscles, but nobody really knew if these two problems were connected. By measuring actual blood vitamin D levels and testing real muscle strength in a diverse group of people, the researchers could see if there was a meaningful relationship. Understanding this connection helps doctors know whether vitamin D supplementation might be an important part of care for dialysis patients.

Strengths: The study measured actual blood vitamin D levels rather than just asking people about their diet, and used a precise test for muscle strength. The group included people from different ethnic backgrounds, which is good. Limitations: The study only looked at people in one city at one point in time, so results may not apply everywhere. People had to remember what they ate for three days, which can be inaccurate. Because it’s cross-sectional, we can’t prove that low vitamin D causes weak muscles—only that they’re connected.

What the Results Show

Nearly half of the study participants (47%) had weak hand grip strength for their age and sex. About one-quarter (25%) had vitamin D deficiency. The key finding was that people with low vitamin D were more than five times more likely to have weak grip strength compared to those with normal vitamin D levels. This was a strong connection that held true even after accounting for age, sex, and body weight.

People who took vitamin D supplements had significantly higher vitamin D levels in their blood than those who didn’t take supplements. Interestingly, almost everyone in the study (97%) wasn’t getting enough vitamin D from food alone, but this dietary intake wasn’t directly connected to muscle strength. What mattered more was whether people were taking supplements to boost their vitamin D levels.

The study found that vitamin D supplementation was associated with higher blood vitamin D concentrations. People who reported taking supplements had better vitamin D status overall. However, the study didn’t find a direct link between how much vitamin D people got from food and their muscle strength—suggesting that food sources alone may not be enough for this population, and supplements may be necessary.

Previous research has shown that both weak muscles and low vitamin D are common problems in kidney dialysis patients, but the connection between them wasn’t well understood. This study adds to growing evidence that vitamin D may play a role in muscle health. The findings align with other research showing vitamin D is important for bone and muscle function in general populations, and now suggests this may be especially important for dialysis patients.

This study has several important limitations. It only looked at people in Toronto at one specific time, so results may not apply to dialysis patients in other places or different time periods. The study design can’t prove that low vitamin D causes weak muscles—only that they’re connected. People had to remember what they ate for three days, which is often inaccurate. The study was relatively small (81 people), so larger studies are needed to confirm these findings.

The Bottom Line

For kidney dialysis patients: Ask your doctor to check your vitamin D levels and discuss whether vitamin D supplements are right for you. The evidence suggests maintaining adequate vitamin D may support muscle strength. Confidence level: Moderate—this study shows a strong connection, but more research is needed to prove supplements will definitely help. For healthcare providers: Consider vitamin D screening and supplementation as part of comprehensive care for dialysis patients, particularly those with weak muscles.

This research is most relevant to people receiving kidney dialysis treatment, especially those experiencing muscle weakness. It may also interest nephrologists (kidney doctors) and dialysis center staff. People with healthy kidneys should not assume these findings apply to them, as kidney disease changes how the body handles vitamin D. Anyone considering vitamin D supplements should discuss it with their doctor first.

If vitamin D supplements are started, it typically takes several weeks to months to see changes in blood vitamin D levels. Improvements in muscle strength may take even longer—usually several months of consistent supplementation. Results vary by individual based on starting vitamin D level, supplement dose, and other health factors.

Want to Apply This Research?

  • Track weekly hand grip strength using a home grip strength meter (available inexpensively online) and record results in the app. Also log vitamin D supplement doses taken daily and any blood test results showing vitamin D levels when available.
  • Set a daily reminder to take your vitamin D supplement at the same time each day (such as with breakfast). Use the app to log each dose taken and set a weekly goal of 7 consecutive days of supplement adherence.
  • Create a monthly summary view showing: (1) supplement adherence percentage, (2) grip strength trend over time, and (3) notes from doctor visits about vitamin D blood levels. Share this data with your healthcare team during dialysis appointments to track progress and adjust supplementation if needed.

This research applies specifically to people receiving kidney dialysis treatment and should not be applied to the general population or people with healthy kidneys. Vitamin D supplementation decisions should always be made in consultation with your nephrologist or kidney specialist, as kidney disease affects how your body processes vitamin D and certain nutrients. This study shows a connection between vitamin D and muscle strength but does not prove that supplements will definitely improve your strength. Do not start, stop, or change any supplements without discussing with your healthcare provider first. This information is for educational purposes and is not a substitute for professional medical advice.